Manufacture or peroxid of lead.



No. 734,950. PATENTED JULY 28, 1903.

B. QUBDENFELDT. MANUFACTURB 0F PEROXID 0F LEAD. l,APPLICATION FILED JUNE25, 19o1.

No MQDBL.

fafk au H UNITED STATES Patented lTuly 28, 1903.

PATENT OEEICE.

ERWIN QUEDENFELDT, OF DUISBURG, GERMANY, ASSIGNOR TO CHEM- ISCHE FABRIKGRIESHEIM ELEOTRON, OF FRANKFORT-ON-THE-MAIN,

GERMANY.

MANUFACTURE OF PEROXID OF LEAD.

SPEQIFICATION forming part of Letters Patent No. 734,950, dated July 28,1903.

` Application filed June 25, 1901. Serial No. 65,993. (No specimens.)

of Lead, of which the following is a specifica-v tion.

The process forming the subject ofthe present invention is characterizedby the direct conversion of lead oxid (litharge, red lead, and the like)into lead dioxid. This conversion is effected in a concentrated solutionof an alkali chlorid or of a chlorid of an alkaline earth forming anemulsion with the lead oxid, the mixture being electrolyzed at apressure of about three volts and a corresponding current intensity b vmeans of'an insoluble anode-such as platinum, carbon, or the like-and acathode of any metal, which is preferably fitted int-o a frame overwhich parchment-paper or other suitable materi al is stretched, or whichis separated fromv the anode by any other suitable diaphragm. No traceof chlorin is evolved at the anode,

while a brisk disengagement of hydrogen takes place on the cathodewithout any appreciable deposit of spongy lead. The lead oXid, which iskept in constant motion, becomes gradually brown and toward the end ofthe electrolytic process becomes black brown. The conversion of the leadoxid into superoxid takes place quantitatively in the time calculatedfrom the current intensity required for the oxidation. By shortening thetime of this reaction it is possible to obtain in the reaction productany required amount of lead dioXid.

The transformation of lead oxid into peroXid by this process is asfollows: Lead oXid being but very imperfectly oxidized todioxid byhypochlorous salts, it is to be supposed that in the presentelectrolytic process the hypochlorite that is formed does not actdirectly on the lead oXid contained in the emulsion, but on the compoundof alkali and lead oxid,

ONa (Pb/ \oNaJ which must be formed as an intermediate product and passinto the solution. In th'is resides the great advantage possessed bythis process over those hitherto known, for according to the oldermethods a salt of lead in solution must always be caused to act on thehypochloroussalts, so as to obtain a large percentage of dioXid, thissalt being either lead chlorid or lead acetate; but with the processforming the subject of. this invention no special preliminary dissolvingoperation, either in acetic acid or hydrochloric acid, is needed, forthe alkali, which is always present in small quantities in the presentelectrolytic process, will dissolve corresponding quantities of thecompound of alkali and lead oXid, which are then at once converted bythe hypochlorite or by chlorin into lead dioxid and alkaline chlorid, asthe following equation shows:

ONaOl Pb/ An advantage possessed by the improved electrolytic processover those hitherto known is that the dioXid is not deposited directlyon the anode, which would cause it to be of crystalline texture, andthat being formed in a state of emulsion it assumes a perfectlypulverulent form.

In the accompanying drawings is illustrated one form of apparatus whichmay be used, and in whichl Figure l is a vertical sectional view of theapparatus, and Fig. 2 is a plan view thereof.

The new process may be carried out as follows: An earthenware vessel ais provided, containing a concentrated solution'of alkaline chlorid orof a chlorid of alkaline earth, in which is placed an anode b, which mayconsist of platinum or carbon, and cathodes c and d, of iron, mounted inWooden frames e and f, having parchment -skin g and 7L stretched overthem. The earthen vessel is placed in a water-bath lo, heated by asteamcoil t', a stirring device Zkeeping in constant y motion the leadoXid held in suspension in the solution. After the electric current hasacted for a time calculated according to the IOO amount of the lead oxidand current intensity used the solution and the finely-dividedbrown-black dioxid contained in its mass'are drawn o into depositingvessels. The solution that has become clear is returned to the reactionvessel, mixed with litharge, and electrolyzed again. Theblack-brownmuddy deposit of dioxid is washed several times with Waterand is finally dried. The dioxid forms then a black-brown powder in anexceedingly fine state of division.

This process diers, essentially, from the electrolytic oxidation processof lead oxid, which involves the use of a solution of an alkalinesulfate as, electrolyte. This difference is partly one of a purechemical nature. When sulfates are decomposed electrolytically, alkaliis produced at the cathode, while sulfuric acid and oxygen appear at theanode. The sulfuric acid and the alkali combine again to form a sulfate,while the oxygen escapes in the gaseous form. The electrolysis ofchlorids and other haloid salts takes place in such a manner that analkali is likewise produced at the cathode; but the halogen appears atthe anode not in the free gaseous form, but as an alkaline salt of a4halogen oxyacid, such as a hypochlorite. The oxidizing agent of the leadis therefore in the first case oxygen in the nascent state and in thesecond case a salt of a halogen oxyacid. With the sulfates the oxidationcan take place only at the anode, while with the haloid salts, owing tothe solubility of the salts of the halogen oxyacid prod uced,theoxidation takes place both at the anode and within the liquid. Thischemical combination of the halogen produces a new and most favorableaction,whereby a direct storage of the oxidizing agent is effected.

It is obvious that when sulfates are used as electrolyte the oxygenliberated at the anode can only oxidize the molecules of lead oxid thatcome in contact with the anode. This is indeed what takes place in aquantitative manner at the commencement of the process; but toward theend of the process the particles of lead dioxid formed predominate tosuch an extent that the nascent oxygen does not meet with a sufficientquantity of lead oxid, so that correspondingquantities of gaseous oxygenescape into the atmosphere. There are therefore losses of current, andif these are to be avoided much less current densities must be usedtoward the end of the process, which densities must in order to avoid.entire losses be decreased constantly inthe ratio of the lead dioxidproduced to the lead oxid remaining. Comparative trials made withsulfates and with chlorids in accordance with the invention have provedthis. This oxidation by means of sulfates proceeds best withanode-plates of very large area; otherwise troublesome preparations areneededsuch as inclosing the anode in a paste of lead oxid, sodiumsulfate, and magnesium sulfate. As regards the special treatment of leadoxid in sulfate electrolyte this is described in the German Patent No.109,823, of September 14, 1898, according to which the lead oxid isplaced in layers on a horizontal anode-plate at the lower part of theelectrolyzing Vessel, so that the oxygen in the nascent state has topenetrate through the thickness of the layer of the lead oxid; butdespite all these precautions current losses are unavoidable. Thepresent invention is free from these disadvantages, for whether or notthe lead oxid is placed at the anode the oxidation takes place withinthe liquid. As the oxidizing agent accumulates in the dissolved form thefollowing Aresults are secured by this invention: First, the area of theanode is of no importance; second, all current losses are avoided, forif the current is greater than is required an excess ot' salts ofhalogen oxyacid is formed, and this excess is utilized for the treatmentof the next portion of lead oxid.

The essential difference between the oxidation of lead oxids in thesulfates is that the oxidizing agent cannot be stored in achemically-bound form, while with the haloid 'salts the oxidizing agentis converted into easily soluble strongly oxidizing combinations, whichtransform the lead oxid into dioxid within the electrolyte, this storagenot causing the least loss of current.

I claim- The herein-described process for the direct conversion of leadoxid into lead dioxid,wl1ich consists in forming an emulsion of the leadoxid with a concentrated solution of an alkali chlorid, subjecting thesame to electrolysis, and keeping the emulsion in motion during theelectrolyt-ic action.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses;

ERWIN QUEDENFELDT.

Witnesses:

JEAN GRUND, FRANZ I-IAssLAcHER.

IOO

